Retarder system

ABSTRACT

A retarder system for commercial vehicles is provided which consists of a transmission oil circuit ( 18 ) for lubrication of the transmission and of a retarder cooling circuit ( 4 ) which uses oil as operating fluid, both circuits being coupled via a connection ( 21 ) so that in the non-activated braking state of the retarder ( 1 ), for increasing the transmission oil flow rate through a radiator ( 3 ), oil can be branched off from the transmission oil circuit ( 18 ). In addition a retarder pump ( 12 ) is proposed which has a prime mover ( 25 ), preferably an electrical motor.

FIELD OF THE INVENTION

The invention relates to a retarder system.

BACKGROUND OF THE INVENTION

Hydrodynamic retarders have become known, for example, from the Germanpublication. Dubbel, “Taschenbuch für den Maschinenbau”, 18^(th)edition, pages R49-R53. Those retarders are connected and disconnectedby filling and emptying with an operating fluid a bladed working cycle.

Mainly commercial vehicles have a hydrodynamic retarder with a retardercoolant circuit. Even though said retarder coolant circuit is designedseparate from the transmission oil circuit proper, it uses as a rule thetransmission oil from the transmission sump as operating fluid.

Retarders are often used as wear-resistant continuously operating brakeswhich are provided with a rotor unit connectable with the transmissionof the vehicle and for decelerating the vehicle converts the mechanicalenergy of the transmission to thermal energy. It is, therefore, obviousto use the transmission oil as operating fluid of the retarder.

In DE 197 51 776 A1 and DE 196 46 598 A1, for example, hydrodynamicretarders of that kind have been disclosed in which the rotor convertsthe mechanical energy to the energy of a fluid which for its part ischanged to heat in the rotor unit whereby the desired braking power isproduced.

Hydrodynamic retarders can be either coupled to the transmission to bedecelerated or already integrated in it. In a common arrangement of thehydrodynamic retarder this is integrated in a transmission, preferablyof commercial vehicles, and driven by a drive shaft of the transmission,the operating fluid constituting, as already mentioned, oil from atransmission sump which simultaneously feeds a separate transmission oilcircuit.

In construction and operation a retarder is similar to a hydrodynamicconverter which is used in opposite working direction. The hydrodynamicretarders, already known, are usually designed with a rotor unit and astator unit, the rotor unit being designed with a rotor shaft and arotor impeller which interacts with a stator impeller disposed spacedfrom the rotor impeller.

The rotor unit of the retarder is here connected with the drive shaft ofthe transmission while the stator unit is fixedly situated on a retarderor transmission housing. As a consequence of the loading with a torquefrom the rotor unit, the operating fluid located between rotor impellerand stator impeller is driven and circulated by the rotor unit,similarly as in a pump, in the working cycle of the retarder. Thehydraulic flow resistance of operation fluid is braking the output shaftof the transmission, a certain differential rotational speed havingalways to be maintained.

The kinetic energy consumed as result of the delay or of thedeceleration of the rotor results in a heating of the transmission oil.To prevent an overheating respectively of the retarder or of the oil,the heated transmission oil has to be cooled off in an adequate mannerwhen passing through a radiator.

To eliminate the heat produced in the retarder, a retarder coolantcircuit is usually provided which comprises the retarder with the statorunit and the rotor unit thereof and the radiator. In the activated stateof the retarder, said retarder coolant circuit is closed as intrinsicworking cycle of the retarder, there being conveyed, via a control valveand a retarder pump, operating fluid which has been lost due to innerleakage in order to maintain the filling level in the system. In adeactivated state of the retarder, the transmission oil is deliveredthrough the radiator by the retarder pump according to the rotationalspeed of the transmission and thus to the velocity of the vehicle whilecircumventing the rotor and stator units of the retarder, and thenreturned to the transmission sump. The radiator in the coolant circuitof the retarder is a heat exchanger known per se which can communicatewith a cooling water system of the motor.

At a low speed of the vehicle, a correspondingly small amount oftransmission oil is passed through the heat exchanger. Since the degreeof cooling power essentially depends on the flow rate, the cooling ofthe transmission oil is in those cases rather ineffective and theradiator is marked by a poor degree of efficiency.

In addition in certain driving situations, there exist specific loadconditions which require an increased flow rate of transmission oilthrough the radiator. Here is to be mentioned such a driving situationin which a high working capacity with simultaneous low velocity occursas is the case, for example, in mountain driving of a commercial vehicleunder full load. It is problematic here that in accordance with the lowvelocity of the vehicle, the transmission pump makes available to theradiator only a correspondingly low amount of oil and the cooling powerneeded for this case of load can only be attained by a considerablylarger amount of oil. The degree of efficiency of the radiator is alsolow in this case.

SUMMARY OF THE INVENTION

The problem on which this invention is based is to provide a retardersystem in which with simple means the flow rate of transmission oilthrough a radiator of a retarder can be optionally increased in certaindriving situations that occur for the purpose of obtaining bettercooling power.

The heat exchanger of the retarder coolant circuit is basically laid outfor a multiplicity of flow rates of transmission oil that the retarderpump can make available, as this must always be the case, for example,for the braking state of the retarder, that is, in its closed workingcycle. Consequently an exiting amount of transmission oil exceeding theamount normally flowing through the radiator depending on the prevalentvelocity can always be easily absorbed by the radiator.

According to the invention the flow rate can be optionally increasedwithout this exclusively depending on the actual velocity of thevehicle. According to the invention this is possible for a low velocityof the vehicle both under normal load and under full load or overloadlike, for example, in a mountain drive.

The better cooling power that goes along with an increased flow ratelowers the maximum temperature of the transmission oil occurring duringthe cooling operation whereby the service life of this operating fluidis decisively extended. Besides, the degree of efficiency of the heatexchanger used increases. With an altogether better cooling behavior isalso associated a subsequent re-regulation of the retarder.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 is a diagrammatic view of an inventive retarder system which canbe connected with a transmission oil circuit; and

FIG. 2 is a diagrammatic view of a retarder pump according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, it diagrammatically shows a retarder 1 with theappertaining circuits which is integrated in a transmission, not shownin further detail, of a commercial vehicle.

The retarder 1 in the brake activated state, that is, in a decelerationaction upon the transmission, is connected via a switch valve 2 with aradiator 3 that constitutes a heat exchanger whereby a closed workingcycle or retarder coolant circuit 4 forms. In this closed working cycle4, the transmission oil circulates as operating fluid as result of thetorque applied by a rotor 5 of the retarder 1 when the transmission isdecelerated. In the radiator 3, which is connected with a symbolicallyshown motor cooling system 6, the transmission oil heated by theretarder 1 is cooled off while the heat is radiated to a motor coolingwater.

The retarder 1, in a non-activated state, is emptied of transmissionoil. In order to be able to start up, a specific starting amount oftransmission oil is needed which is briefly made available by an oilaccumulator 7 after the switch valve 2 closes the working cycle 4. Whenthe retarder 1 is activated, the oil accumulator 7 is actuated by thedriver by means of a compressed air device 26 only indicated here, theneeded amount of transmission oil being pumped into the working cycle 4so that the retarder 1 can start up.

The braking power of the retarder 1 depends essentially on the amount oftransmission oil available in the retarder 1 or in the working cycle 4.The braking power is selected by the driver via a brake steppedselection 8 with a stepped regulation. To this end is provided a controlvalve 9 which is connected with the brake stepped selection 8 and, inturn, acts upon a regulating valve 10. Said regulating valve 10communicates on one side, via a feed line 11, with the working cycle 4and on the other side, via a retarder pump 12, with a transmission sump13. The amount of transmission oil corresponding to one selected brakingstep and thus to a certain braking power is delivered by the retarderpump 12 out of the transmission sump 13 and supplied via the regulatingvalve 10 to the working cycle 4. The retarder pump 12 is connected withthe output of the transmission so that the delivery work takes place inaccordance with the rotational speed of the transmission and thus withthe velocity of the commercial vehicle.

During the braking operation of the retarder 1, the retarder pump 12 andthe regulating valve 10 constantly feed a certain amount of transmissionoil to the working cycle 4 in order to balance the leakage lossesoccurring in the retarder 1 and returned by inner leakage (graphicallyshown by line 14) to the transmission sump 13.

When the retarder 1 is in a non-activated braking state, the switchvalve 2, as diagrammatically shown with dotted lines in FIG. 1, isshifted so that the radiator 3 communicates, via a feed line 15,directly with the retarder pump 12 and the transmission sump 13. Afterthe radiator 3, the transmission oil delivered by the retarder pump 12is again returned to the transmission sump 13, via the exhaust line 16.The exhaust line 16 has a pressure retaining valve 17 in order tomaintain (relative to the radiator 3) a specific counter-pressure forpurposes of an adequate operation.

In addition, a transmission oil circuit 18 branches off from thetransmission sump 13 by which the transmission oil arrives at asymbolically shown transmission lubrication device 19. The amount oftransmission oil needed for lubrication of the transmission is madeavailable by a transmission pump 20 in the manner of oil delivery pumpsknown per se. During normal operation, the transmission pump 20 worksaccording to the rotational speed of the transmission.

According to the invention, a connection 21 is provided from thetransmission oil circuit 18 to the retarder coolant circuit 4 so that,in addition to the amount delivered by the retarder pump 12, additionaltransmission oil can be supplied from the transmission oil circuit 18 tothe radiator 3 while increasing the cooling power. Since the retarder 1is not activated for braking, the retarder coolant circuit 4 is herelocated in an open position, that is, the retarder 1 is circumvented.

The branching off of the amount of transmission oil needed forlubrication of the transmission, on one hand, and the relay of addedtransmission oil to the retarder coolant circuit 4, on the other, areensured according to the invention by a distributor block 22 which canhave several valves of conventional design. The distributor block 22 orthe valves thereof are electronically controllable, their openingbehavior resulting according to the oil temperature and to the loadstate of the transmission.

The connection 21, the same as the feed line 15 of the retarder coolantcircuit 4, have respective recoil (one way) valves 23 and 24 whichprevent a return of transmission oil in a direction opposite to thedelivery direction of the transmission oil.

FIG. 2 shows diagrammatically and only in section one other embodimentof the invention.

The desired increase of the flow rate of transmission oil through theradiator 3 can also be implemented by coupling the retarder pump 12 witha prime mover 25, usually electrical and located outside thetransmission, which preferably can be electronically controlled. Theretarder pump 12, which otherwise is coupled to the transmissiondepending on the output rotational speed is, according to thisembodiment, uncoupled from the transmission and driven by the electricalmotor 25 so that independent of the output rotational speed of thetransmission, an altogether higher delivery rate can be obtained. Thetransmission oil thus delivered out of the transmission sump 13 issupplied to the switch valve 2 and the radiator 3, via the feed line 15,and returned from the radiator 3, via the exhaust line 16 and thepressure-retaining valve 17, again supplied to the transmission sump 13and always circumventing the retarder 1.

Both embodiments of the invention, that is, the connection 21 of thetransmission oil circuit 18 with the retarder coolant circuit 4 and thecoupling of the retarder pump 12 with the additional prime mover 25, canobviously be combined in one whole system.

In all embodiments the control or regulation of the transmission pump20, of the distributor block 22 or the valves contained therein and ofthe retarder pump 12 with the prime mover 25 is ideally connected withan electronic transmission control and laid out according to parameters,specially according to load and/or temperature.

What is claimed is:
 1. A retarder system for a motor vehicle having aretarder coolant circuit (4) comprising: a retarder (1); a radiator (3);a retarder pump (12) for supplying transmission oil from a transmissionsump (13) to the radiator (3); at least one of a control valve (9) and aregulating valve (10) for regulating flow of transmission oil requiredby the retarder (1) as an operating fluid when preforming requiredbraking; and a switch valve (2), when in a first position in which theretarder (1) is in an inactive state, connecting the retarder pump (12)with the radiator (3) so that the transmission oil, supplied from thetransmission sump (13), is returned to the transmission sump (13) viathe radiator (3) without passing through the retarder (1) and the switchvalve (2), when in a second position in which the retarder (1) is in anactive state, connecting the radiator (3) with the retarder (1) forforming a closed loop cooling circuit (4); wherein a transmission oilcircuit (18) has a transmission pump (20) for supplying transmission oilfrom the transmission sump (13) to at least one other component of thetransmission for lubrication thereof, and the transmission oil circuit(18) has a connection (21) with the retarder cooling circuit (4) suchthat transmission oil can be branched off from the transmission oilcircuit (18) for increasing the flow rate of transmission oil throughthe radiator (3); and a one way valve (23) is provided along thetransmission oil flow path, between the retarder pump (12) and theretarder cooling circuit (4), to prevent transmission oil from flowingback toward the transmission sump (13), and a one way valve (24) isprovided along the transmission oil flow path, between the transmissionpump (20) and the retarder cooling circuit (4), to prevent transmissionoil from flowing back toward the transmission sump (13).
 2. The retardersystem according to claim 1, wherein a flow rate of transmission oilsupplied by the retarder pump (12) is dependent upon the velocity of thevehicle and a flow rate of transmission oil supplied by the transmissionpump (20) is dependent upon the rotational speed of the transmission. 3.A retarder system for a motor vehicle having a retarder coolant circuit(4) comprising: a retarder (1); a radiator (3); a retarder pump (12) forsupplying transmission oil from a transmission sump (13) to the radiator(3); at least one of a control valve (9) and a regulating valve (10) forregulating flow of transmission oil required by the retarder (1) as anoperating fluid when preforming required braking; and a switch valve(2), when in a first position in which the retarder (1) is in aninactive state, connecting the retarder pump (12) with the radiator (3)so that the transmission oil, supplied from the transmission sump (13),is returned to the transmission sump (13) via the radiator (3) withoutpassing through the retarder (1) and the switch valve (2), when in asecond position in which the retarder (1) is in an active state,connecting the radiator (3) with the retarder (1) for forming a closedloop cooling circuit (4); wherein a transmission oil circuit (18) has atransmission pump (20) for supplying transmission oil from thetransmission sump (13) to at least one other component of thetransmission for lubrication thereof, and the transmission oil circuit(18) has a connection (21) with the retarder cooling circuit (4) suchthat, when the retarder (1) is in the inactive state, transmission oilcan be branched off from the transmission oil circuit (18) forincreasing the flow rate of transmission oil through the radiator (3);and the transmission oil circuit (18) has a distributor block (22) whichregulates the supply of transmission oil to the transmission and to theradiator (3).
 4. The retarder system according to claim 3, wherein thedistributor block (22) is electronically controlled by the retardersystem according to at least one of load, a temperature and a velocity.5. The retarder system according to claim 3, wherein a flow rate oftransmission oil supplied by the retarder pump (12) is dependent uponthe velocity of the vehicle and a flow rate of transmission oil suppliedby the transmission pump (20) is dependent upon the rotational speed ofthe transmission.
 6. A retarder system for a motor vehicle having aretarder coolant circuit (4) comprising: a retarder (1); a radiator (3);a retarder pump (12) for supplying transmission oil from a transmissionsump (13) to the radiator (3); at least one of a control valve (9) and aregulating valve (10) for regulating flow of transmission oil requiredby the retarder (1) as an operating fluid when preforming requiredbraking; and a switch valve (2), when in a first position in which theretarder (1) is in an inactive state, connecting the retarder pump (12)with the radiator (3) so that the transmission oil, supplied from thetransmission sump (13), is returned to the transmission sump (13) viathe radiator (3) without passing through the retarder (1) and the switchvalve (2), when in a second position in which the retarder (1) is in anactive state, connecting the radiator (3) with the retarder (1) forforming a closed loop cooling circuit (4); wherein a transmission oilcircuit (18) has a transmission pump (20) for supplying transmission oilfrom the transmission sump (13) to at least one other component of thetransmission for lubrication thereof, and the transmission oil circuit(18) has a connection (21) with the retarder cooling circuit (4) suchthat, when the retarder (1) is in the inactive state, transmission oilcan be branched off from the transmission oil circuit (18) forincreasing the flow rate of transmission oil through the radiator (3);and the retarder pump (12) is coupled with a prime mover (25) so as tobe controlled independently of a velocity of the vehicle.
 7. Theretarder system according to claim 6, wherein the prime mover is anelectrical motor (25).
 8. The retarder system according to claim 6,wherein the prime mover (25) is electronically controlled in accordancewith an actual operating condition.